Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 7: Transcendental Functions - Practice Exercises - Page 440: 76

Answer

$$\frac{{\sqrt 3 }}{4}\pi $$

Work Step by Step

$$\eqalign{ & \int_{ - 1}^1 {\frac{{3dv}}{{4{v^2} + 4v + 4}}} \cr & = \frac{3}{4}\int_{ - 1}^1 {\frac{{dv}}{{{v^2} + v + 1}}} \cr & {\text{Complete the square for }}{v^2} + v + 1 \cr & {v^2} + v + 1 = {v^2} + v + \frac{1}{4} + \frac{3}{4} \cr & {v^2} + v + 1 = {\left( {v + \frac{1}{2}} \right)^2} + \frac{3}{4} \cr & = \frac{3}{4}\int_{ - 1}^1 {\frac{{dv}}{{{{\left( {v + 1/2} \right)}^2} + 3/4}}} \cr & {\text{Use the substitution method}} \cr & u = v + 1/2,\,\,\,\,\,\,du = dv \cr & {\text{The new limits on }}u{\text{ are found as follows}} \cr & \,\,\,\,\,\,{\text{If }}v = 1,{\text{ then }}u = 1 + 1/2 = 3/2 \cr & \,\,\,\,\,\,{\text{If }}v = - 1,{\text{ then }}u = - 1 + 1/2 = - 1/2 \cr & {\text{Then}} \cr & \frac{3}{4}\int_{ - 1}^1 {\frac{{dv}}{{{{\left( {v + 1/2} \right)}^2} + 3/4}}} = \frac{3}{4}\int_{ - 1/2}^{3/2} {\frac{{dv}}{{{u^2} + {{\left( {\sqrt 3 /2} \right)}^2}}}} \cr & {\text{integrating by the formula }}\int {\frac{1}{{{u^2} + {a^2}}}du} = \frac{1}{a}{\tan ^{ - 1}}\left( {\frac{u}{a}} \right) + C.{\text{ with }}a = \sqrt 3 /2 \cr & \frac{3}{4}\int_{ - 1/2}^{3/2} {\frac{{dv}}{{{u^2} + {{\left( {\sqrt 3 /2} \right)}^2}}}} = \frac{3}{4}\left( {\frac{2}{{\sqrt 3 }}{{\tan }^{ - 1}}\left( {\frac{{2u}}{{\sqrt 3 }}} \right)} \right)_{ - 1/2}^{3/2} \cr & = \frac{{\sqrt 3 }}{2}\left( {{{\tan }^{ - 1}}\left( {\frac{{2u}}{{\sqrt 3 }}} \right)} \right)_{ - 1/2}^{3/2} \cr & = \frac{{\sqrt 3 }}{2}\left( {{{\tan }^{ - 1}}\left( {\frac{{2\left( {3/2} \right)}}{{\sqrt 3 }}} \right) - {{\tan }^{ - 1}}\left( {\frac{{2\left( { - 1/2} \right)}}{{\sqrt 3 }}} \right)} \right) \cr & {\text{simplify}} \cr & = \frac{{\sqrt 3 }}{2}\left( {{{\tan }^{ - 1}}\left( {\sqrt 3 } \right) - {{\tan }^{ - 1}}\left( { - \frac{{\sqrt 3 }}{3}} \right)} \right) \cr & = \frac{{\sqrt 3 }}{2}\left( {\frac{1}{3}\pi + \frac{1}{6}\pi } \right) \cr & = \frac{{\sqrt 3 }}{2}\left( {\frac{\pi }{2}} \right) \cr & = \frac{{\sqrt 3 }}{4}\pi \cr} $$
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